We visited the subject's neighbourhood when he was seven years old, and playing a game of 'street cricket' with his friends. Having procured the details of every person, creature, and event for several blocks around thanks to my nano recorders, we could time things perfectly.

Mrs. Doran and I ensconced ourselves in a vacant house, the owners having gone on holiday. I gave Mrs. Doran a dart gun, indicated the target, and counted down to when she had to fire. She is a crack shot, and the dog barely noticed the slight twinge in its back caused as the projectile struck, then melted into the animal's bloodstream, releasing a minute amount of toxin into it, slowing the creature's movements just enough.

When the vehicle came down the street, the children got out of its way, the dog was marginally slower.

The sight of our client as a child, cradling his dying pet and crying, well it warmed the cockles of our hearts. The first step for giving him misery, a sense of perspective, and therefore a counterpoint to all that was right within his world, had been made.

Of course any replacement pets purchased by the client's family will also have to be dealt with.

Once we were sure things had progressed according to plan, we then had to pop forward a few years, and arrange for a near identical dog to alert locals that a boy called Timothy was trapped in a stormwater drain. Twenty years on, Timothy would go on to be an assistant to the head of a chemical company. He would give the owner incorrect advice, resulting in the company eventually having to be sold. The new owners would fail to continue the excellent maintenance standards of the previous regime, leading to a catastrophic leak that would kill hundreds of people and introduce small genetic changes in the offspirng of several hundrd families. Those changes would carry on through the generations... and so on.

Now we could merely have saved the Timothy's life ourselves, but I find that keeping events as close as possible to the original timeline is the best method. For instance, while the saving of Timothy's life has a rather obvious side effect in the long term, there are also the effects of the story being published in the newspaper, complete with a photograph of the child and his canine saviour. Because a photograph of a boy and a dog is much more interesting than a boy and another humanoid, another story got bumped to a different page to make room for said picture. Literally hundreds of people will now miss seeing the other story, and many that would have missed it will now happen across it because by arranging for the dog, it is where it was meant to be.

The effect of the picture goes beyond that, of course. That photograph caused some people to choose to buy that particular breed of animal when next looking for a pet. That effects the finances and lifestyles of numerous people and families, stores that sell dog food, veterinarians that care for the animals, native wildlife that gets eaten, etc.

There are other, more subtle changes, but you get the general concept.

It's why I do so hate most time travellers, they really don't comprehend the full extent of even a minor change.